Liquid crystal displays are used for personal computers, TVs, monitors, cellular phones, PDAs, and so on. Dyed polyvinyl alcohol films have been used for polarizers of liquid crystal displays and so on, because they have a high level of both transmittance and degree of polarization. For example, such polarizers are produced by a process that includes subjecting a polyvinyl alcohol film to each of swelling, dyeing, crosslinking, and stretching processes in a bath, then subjecting the film to a washing process, and then drying the film. Such polarizers are generally used in the form of polarizing plates, which are each composed of a polarizer and a protective film, such as a triacetylcellulose film, bonded to one or both sides of the polarizer with an adhesive.
In recent years, liquid crystal displays have become more sophisticated, and liquid crystal panels are required to have higher contrast such that high visibility can be achieved. Specifically, blacker in black viewing and whiter and brighter in white viewing are desired, and, therefore, further improvement in the polarization performance of polarizers is required. Accordingly, satisfying both high degree of polarization and high transmittance has become very important for polarization performance.
In order to obtain such polarizers, a large number of methods have been proposed. For example, a proposed method for producing polarizers includes subjecting a polyvinyl alcohol film to each of swelling, dyeing, crosslinking, and stretching processes, then subjecting the film to iodide ion treatment as a washing process, and then immersing the film in an alcohol solution (see Patent Literature 1). According to Patent Literature 1, the moisture percentage of polarizers can be reduced without heating, and drying are possible with no degradation in the optical properties of polarizers.
The polarizer is used to form a polarizing plate for liquid crystal displays. Therefore, the polarizer needs to be durable so that its optical properties can resist change even under healing or humidifying conditions. The polarizer also needs to have the initial optical properties over a wide band.
Patent Literature 1: JP-A No. 2003-270440